Device and method for pressing a plastically deformable blank

ABSTRACT

The invention concerns a device and a method for continuous pressing of a plastically deformable blank into a three-dimensional section with a predetermined cross-sectional area, comprising a substantially cylindrical, fixed die, an opening formed in the die, through which the plastic blank is intended to be pressed, and at least one rotary die arranged adjacent to the opening, the rotary die having one or more recesses in its peripheral surface for forming the blank, during the rotation of the die, into a three-dimensional section with transverse sectional parts. According to the invention, the rotary die is arranged immediately downstream of the opening, whereby the blank is reducible, when passing through the opening, substantially down to the predetermined cross-sectional area, and formable, when passing the rotary die, thereby determining the final shape of the three-dimensional section. furthermore, the device is compatible with conventional extrusion machines in order to allow rapid switching of tools with no need for expensive production stop-pages.

TECHNICAL FIELD

The present invention relates to a device and a method for continuouspressing of a plastically deformable blank, for example made of a metal,into a three-dimensional section with a predetermined cross-sectionalarea, comprising a fixed die with an opening formed in the die, throughwhich the plastically deformable blank is intended to be pressed, and atleast one rotary die arranged, adjacent to the opening, around an axisextending transversely of the press direction, the die having one ormore recesses in its peripheral surface for forming the blank into athree-dimensional section with transverse sectional parts during therotation of the rotary die.

TECHNICAL BACKGROUND

In continuous pressing of a plastically deformable blank, for example aheated metal such as aluminium, so-called extrusion, the blank passes anopening with a desired cross-sectional area, thereby forming a sectionwhose longitudinal cross-section is constant. There is a great need forcontinuous manufacture of sections with transverse sectional parts, suchas racks, hollow sections, etc.

International Patent Specification WO97/12745 discloses a method and adevice invented by the present inventor, which aim at allowing extrusionof sections with sectional parts protruding transversely of the section.According to this publication, a rotary die is arranged to constitutepart of the opening through which the blank is pressed. As thecross-sectional area of the blank is being reduced, the rotating diesimultaneously forms it. The rotary die can be designed to producetransverse bars in the section, or to form a raised or embedded companyname in the section.

The difference compared to various types of die stamping with rotatingelements is to be noted, illustrated for example in DE 42101746, whereonly a very limited forming of the blank takes place. When shapingaccording to the above technique, as referred to by the presentinvention, the rotating die forms part of the actual extrusion process.

The application of this technique in existing, largely standardised,press facilities such as hydraulic pressing plants, screw extruders,conform extrusion machines, etc, was previously impossible. Facilitiesof said type usually comprise a tool arrangement of the type shown inFIG. 2, with a support 5 for a substantially cylindrical tool 3comprising a fixed die 1. There is not much space around this tool, andthe forces generated during the pressing are very strong.

Furthermore, it is very important that the number of productionstoppages be reduced, since the cost of unexploited machine capacity isvery high. It is, therefore, desirable that tools can be changed rapidlyaccording to pressing needs.

Since Patent Specification WO97/12745 was published, the need forsections with a cross-sectional area that varies longitudinally hasarisen, i.e. a section having not only transverse sectional parts suchas bars, but also a varying cross-section or material thickness alongthe continuous section.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for pressingthree-dimensional sections, which is easy to apply to moulds accordingto prior art, with no need for major adjustments.

This object is achieved by means of a device and a method of the typedescribed by way of introduction, wherein said rotary die is arrangedimmediately downstream of said opening, whereby the blank is reducedwhen passing through said opening (11) to substantially thepredetermined cross-sectional area, and then formed when passing saidrotary die, thereby determining the final shape of the three-dimensionalsection.

Unlike prior art, the area of the blank is thus reduced substantiallydown to its final cross-sectional area upstream of the rotating die,whereby the forces acting on the rotating die can be minimised. Thisresults in manageable bearing forces, which allows the bearings of therotary die to be contained in the fixed die. The expression“substantially down to” means primarily down to between 100% and 130% ofthe final pre-determined cross-sectional area.

The blank meets with the rotating die radially within its averageradius. In this way, some area reduction still takes place at therotating die, and thus a certain acceleration of the blank occurs duringthis passage while at the same time the material fills cavities in therotating die.

The expression “immediately downstream of” means that the rotary die islocated so close to the opening that the pressure of the pressing isused in the shaping done by the rotating die. If the distance is toolong, for example several times the across corner dimension of thesection, the blank will self-lock adjacent to the rotating die becauseof the friction caused upstream against the supporting surfaces when therotating die is in a pressing phase.

The rotary die is preferably mounted in bearings in a transverse cavityformed next to the opening, thereby being rotatable around an axisextending transversely of the pressing direction.

This design of the fixed die allows a space-efficient location of therotary die within the machine. Furthermore, this construction means thatthe rotary die is easily accessible, since it is relatively easy toloosen and remove the tool in a normal compression moulding machine.Thus, the device can be designed so as to be compatible withconventional extruding machines in order to allow rapid changing oftools without the need for expensive production stoppages.

By forming a cavity in the fixed die, the space is used as much as ispossible, and, in addition, a smaller amount of toughened material isneeded for the fixed die, which reduces the cost.

The rotary die is preferably mounted in bearings with a certain axialplay. This play allows some thermal expansion of the rotating diewithout causing any jamming.

The rotary die may be fixedly arranged on a shaft mounted in bearings inthe cavity, the shaft having a limited axial play. Thus, owing to thisconstruction the shaft is axially guided by the rotary die. Since theshaft and its bearings are arranged in the fixed die, this constitutes aunit in which the rotary die is arranged, the unit being easilyreplaceable. Moreover, the shaft may be relatively short, which resultsin a favourable load take-up capacity and less load on the bearings.

A shaft portion extending through the rotary die can be made of amaterial with a higher thermal expansion coefficient than the rotarydie, so that said shaft portion, when the rotary die and the shaft areheated during pressing, expands more than the rotary die, which isthereby secured to the shaft. By using this technique to secure therotary die, the need for securing elements in the shaft and the die iseliminated.

The opening preferably comprises a recess in the fixed die on theupstream side, which is intended to cause a first cross-sectionalreduction of the material, the recess being substantially formed on theside of the opening opposite to the cavity. By forming the recess inthis way, there is less stress on the fixed die at the cavity in whichthe rotary die is arranged. In a traditional type of tool, where thecorresponding recess usually is symmetrical, the material around thecavity may become too thin.

According to a second aspect of the invention, the device furthercomprises means for varying the cross-sectional area immediatelyupstream of the rotary die. In other words, the fixed die is arranged tohave an opening with a variable cross section. Thus, the amount ofmaterial pressed against the rotary die may be varied, suitablyaccording to the shape of the rotary die.

The peripheral surface of the rotary die may, for example, presentsectors with varying radius, which permits pressing of sections withvarying cross-sectional area.

By “peripheral surface” is here meant the normally circular-cylindricalsurface in which different kinds of recesses or protrusions have beenmade for forming the sections, for example the surface that is made upby the pitch radius of a gear wheel. The fact that the radius of theperipheral surface varies could mean, for example, an oval-shaped die(such as a gear wheel with varying pitch radius), or that the shaft isarranged in connection with the rotary die slightly offset relative tothe centre of the die. This would result in a section, whose continuousmaterial thickness would vary cyclically, which is desirable whenmanufacturing a beam with varying strength.

The means for varying the cross-sectional area are suitably synchronisedwith the rotary die and may consist of supporting surfaces moveabletransversely of the pressing direction.

According to a third aspect of the invention, the rotary die is arrangedto be lockable in a predetermined position. Thus, the rotary, moveabledie may be locked, and thereby essentially converted into a fixed die.Pressing may now take place, either by passing one rotary-die or bypassing one or more fixed dies, which offers improved possibilities ofvarying the pressed sections.

The rotary die may suitably have smooth sectors, which in the lockedposition face the blank, so that, in this position, the blank passes thelocked die for forming a smooth sectional segment. By orienting a smoothsector so that it faces the blank when locking the rotary die, theforces acting on the rotary die in the locked position are minimised.Locking the rotary die in a position where recesses or protrusions areoriented so that they face the blank would in fact require a greatlocking force and would, in addition, mean a risk of loose piecesforming in the cavities of the die during pressing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail below withreference to the accompanying drawings, which by way of exampleillustrate preferred embodiments of the invention.

FIG. 1 is a schematic representation of an example of an extrudingmachine.

FIG. 2 is an exploded view of a tool arrangement in an extrudingmachine.

FIG. 3 is a rear perspective view of a die according to a firstembodiment of the invention.

FIG. 4 is a front perspective view of the die in FIG. 3.

FIG. 5 is a cross-sectional view of the die in FIG. 3.

FIG. 6 is a cross-sectional view of the die in FIG. 3 along the lineVI—VI in FIG. 5.

FIG. 7 is a partly exploded view of a die according to a secondembodiment of the invention.

FIG. 8 is a cross-sectional side view of the die in FIG. 7.

FIGS. 9a, b are cross-sectional views of a die according to a furtherembodiment of the invention, with the rotary die in two differentpositions.

FIGS. 10a, b are cross-sectional views of a die according to a furtherembodiment of the invention, with the rotary die in two differentpositions.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a rough schematic representation of a machine intended forextrusion of metals such as aluminium, which have been heated to aplastically deformable state, wherein a ram 6 is arranged by means ofhydraulic actuators 8 to press a blank 15 towards a tool arrangement 7.

FIG. 2 is an exploded view of the tool arrangement 7. The toolarrangement comprises a die 1 which, together with a supporting element2, is arranged in a annular die holder 3 located in front of one or morerear members 4 in a tool support 5 (also called “horseshoe”). The die 1and the supporting element 2 can be replaced by a device according tothe invention, or alternatively the dimensions of the die 10 accordingto the invention may be such that also the die holder 3 is excluded fromthe tool arrangement.

A die unit according to a first embodiment of the invention is shown inFIGS. 3-6. The die unit comprises a substantially cylindrical, fixed die10 with an opening 11 and a rotary die 12. A blank 15 is intended to bepressed through the opening 11 in a pressing direction A. A secondopening 17 is defined between the rotary die 12 and an opposite,preferably plane, supporting surface 18 in the material of the fixed die10. According to the invention, the first opening 11 has across-sectional area that is substantially the same as thecross-sectional area of the second opening 17.

The blank 15 passing the opening 11 is brought in contact with therotary die 12 approximately on a level with its inside radius r1,preferably slightly within the radius r1. If a rotary die 12 in the formof a gear wheel 19 is used, as in the-example shown, r1 designates thepitch radius of the gear wheel, which makes up a peripheral surface fromwhich the gear teeth 21 extend. It is important, regardless of the shapeof the die 12, for the blank to hit the die on such a level that theblank 15 is plastically deformed when passing the rotating die 12. Thedeformation of the blank 15 is shown in more detail in the enlarged viewin FIG. 6.

With reference primarily to FIG. 5, it is shown how the rotary die 12 isrotatable around an axis C. More particularly, it is fixedly mounted ona shaft 23 mounted in bearings in a cavity 20 in the fixed die 10. Thecavity 20 consists essentially of a transverse boring 25 a-c formedbeside the centre axis B of the die and extending transversely of thepressing direction A. The boring 25 a-c has a larger cross section inthe areas 25 a, 25 b, at the respective ends, close to the edge of thedie unit. Immediately inside these areas, the cross section of theboring is smaller, getting larger again, finally, in the most centralpart 25 c. In the areas 25 a, 25 b, two bearings 26 are arranged, forexample roller bearings or slide bearings, through which the shaft 23extends over the whole length of the boring. The die 12 is arranged inthe central area 25 c and fixed laterally by axial bearings 27 arrangedin the area 25 c.

In the example shown, means for cooling the bearings 26 are arranged inthe die unit. The means comprise a ceramic body 22 that is fittedaxially outside each bearing, a seal 24 located outside the body 22, anda supply conduit 12 for a cooling agent, such as nitrogen or the like.

The die 12 is suitably made of a material with a lower thermal expansioncoefficient than at least the central shaft portion 23 a on which it isapplied. In this way, the die 12 is effectively secured when thetemperature of the whole die rises as a result of the extrusion.

With reference to FIG. 3, which is a front perspective view of the fixeddie 10, i.e. as seen from the point from which the blank 15 is pressed,the opening 11 comprises a recess 29 in the die, the recess causing afirst reduction of the area when pressing. This counter-sink 29 isassymetrically shaped in relation to the centre axis B of the die, andthe major part of it is located on the side opposite to the cavity 20.Shaping the recess 29 this way minimises those portions 31 of the diethat are weakened, in the pressing direction A, both by the cavity 20and the recess 29 (see FIG. 6).

It appears from FIG. 4 that the cavity 20 also has an orifice 30 on thefront of the fixed die 10, through which the rotary die 12 is visible.The rotary die 12 is mounted by being inserted through the orifice 30,and then by the shaft 23 being inserted through the boring 25 andthrough the rotary die 12.

According to a second embodiment (FIGS. 7-8) of the invention, a fixeddie 110 comprises two rotary dies 12, 12′, each arranged on a shaft 23,23′ in a boring 25, 25′. This construction permits pressing of sectionsthat are profiled both on the upper side and on the underside.

The two dies may be synchronised with each other in any appropriate way,for example by providing gear wheels to join the shafts 23, 23′. Throughthe synchronisation the distribution of the load take-up between thedies 12, 12′ is improved.

The fixed die 110 further comprises a core die 33 fixedly arranged onthe die 110 and extending through the opening 11, the opening beingdivided in two openings 11, 11′, thereby permitting pressing of a hollowsection. The core die 33, as shown in the perspective view of FIG. 7,comprises, in the embodiment shown, a cruciform portion 34, intended tobe fixedly arranged on the die with the aid of fixing means 35 such asbolts, and an elongated portion 36 intended to extend, once the core dieis arranged on the die, through the opening 11 as far as or past thecentre of the rotary dies. The side 37 of the core die facing the rotarydie 12 thereby replaces the above mentioned supporting surface 18 as theelement defining the opening 17 while at the same time the opposite side37′ defines a second opening 17′.

According to another embodiment of the invention, as shown in FIGS.9a-b, a fixed die 210 comprises a moveable supporting surface 40 inconnection with the rotary die 12. The movable supporting surface 40 iscontrolled by actuators 42 via link means 41, only schematicallyillustrated in FIGS. 9a-b, and is arranged to adjust the opening 11depending on the size of the opening 17 between the rotary die 12 andthe core die 33 (alternatively the supporting surface 18 in the absenceof the core die 33). As shown in FIGS. 9a and 9 b, the supportingsurface 40 may be moved between a first starting position (FIG. 9a), inwhich the opening 11 is essentially the same as in the previouslydescribed embodiments, and a second lowered position (FIG. 9b), in whichthe opening 11 is reduced. This arrangement might be necessary, or atleast advantageous, in situations where the peripheral surface of therotary die has a varying radius, for example when the rotating die 12consists of an oval gear wheel.

In the die 210 shown in FIGS. 9a-b the rotary die 12 is of the same typeas in the above examples, but arranged on the shaft 23 slightly offsetfrom the shaft centre. Thus, as illustrated in FIG. 9a, the material ofthe pressed section gets a larger cross section T1 when the centre X1 ofthe rotary die is located above the shaft centre X2 whereas, asillustrated in FIG. 9b, the material of the pressed section gets asmaller cross section T2 when the centre X1 of the rotary die is locatedbelow the shaft centre X2. The purpose of arranging the supportingsurface 40 to reduce the opening 11 in FIG. 9b is to adapt thecross-sectional area of the blank 15 pressed towards the opening 17 tothe altered cross sections.

Another situation when a moveable supporting surface may be suitable iswhen using a die 310 as shown in FIGS. 10a-b. This die is provided witha rotary die 312 having smooth portions 45, which take up an anglesector that is several times bigger than the usual protrusions (gearteeth). In the example shown, a smooth portion 45 is formed in therotary die 312 taking up about 30 degrees of the circumference of thedie 312. In FIG. 10a pressing is performed in the same way as describedabove, with the supporting surface 40 in the starting position. In FIG.10b, however, the smooth portion has reached the opening 17, which isthus given a reduced cross-sectional area. In order to achieve asatisfactory extrusion also in this position, the supporting surface 40is moved to a lowered position by the actuator 42, whereby the opening11 is reduced.

Furthermore, the die 312 in FIGS. 10a-b may be arranged to be lockablein the position shown in FIG. 10b. When the die is in this lockedposition a straight section without transverse sectional parts can beextruded between the smooth portion 45 of the die 312 and the core die33, alternatively the supporting surface 18.

It is to be noted that FIGS. 9 and 10 are only intended to illustratethe principle behind the described embodiments. A person skilled in theart realises that several of the distances shown in the Figures do notcorrespond to reality, for example in the case of the inclination of thesupporting surface 40, which is exaggerated in order to facilitateunderstanding. As a consequence of this exaggeration also the distancebetween the supporting surface and the rotating die 12, 312 is slightlytoo long.

The rotary dies described above may be arranged, as appropriate, to bedriven, thereby adding extra power to the extrusion process. A personskilled in the art can provide this drive, for example by connecting theshaft 23, 23′ to a driven shaft arranged in the tool support 5. Inparticular, this drive may be advantageous when pressing sections withvarying material thickness, for example as shown in FIGS. 9a, 9 b.

It will be appreciated that details of the embodiments shown in theFigures and described above can be combined in an optional way. Forexample, the core die 33 shown in FIGS. 8, 9 a-b and 10 a-b may beexcluded when pressing solid sections. The number of rotary dies mayvary in all embodiments, and it is mainly for the sake of clarity thatmost Figures show only one die.

What is claimed is:
 1. A device for continuous pressing of a plasticallydeformable blank into a three-dimensional section with a predeterminedcross-sectional area, comprising a fixed die with an opening formedtherein, through which the plastically deformable blank is intended tobe pressed, and at least one rotary die arranged adjacent to the openingand having one or more recesses in its peripheral surface for formingthe blank into a three-dimensional section with transverse sectionalparts during the rotation of the die, wherein: the rotary die isarranged immediately downstream of the opening, the blank beingreducible, when passing through the opening, down to substantially thepredetermined cross-sectional area, and then being formable, whenpassing the rotary die, thereby determining the final shape of thethree-dimensional section.
 2. A device according to claim 1, wherein theblank is reducible, when passing through the opening, down to between100% and 130% of the predetermined cross-sectional area.
 3. A deviceaccording to claim 2, wherein a cavity located next to one side of theopening is formed in the fixed die, and wherein the rotary die ismounted in bearings in the cavity, thereby being rotatable around anaxis extending transversely of the pressing direction.
 4. A deviceaccording to claim 1, wherein a cavity located next to one side of theopening is formed in the fixed die, and wherein the rotary die ismounted in bearings in the cavity (20), thereby being rotatable aroundan axis extending transversely of the pressing direction.
 5. A deviceaccording to claim 4, wherein the rotary die is axially mounted inbearings with a limited axial play.
 6. A device according to claim 5,wherein the rotary die is fixedly arranged on a shaft mounted inbearings in the cavity, the shaft having a limited axial play.
 7. Adevice according to claim 6, wherein a portion (23 a) of the shaft, theportion extending through the rotary die, is made of a material with ahigher thermal expansion coefficient than the rotary die, so that theshaft portion, when the die and the shaft are heated during pressing,expands more than the die, which is thereby secured to the shaft.
 8. Adevice according to claim 4, wherein the fixed die further comprises arecess upstream of the opening, intended to cause a firstcross-sectional reduction of the blank, the recess being substantiallyformed on the side of the opening opposite to the cavity.
 9. A deviceaccording to claim 1, further comprising means for varying thecross-sectional area of the opening immediately upstream of the rotarydie.
 10. A device according to claim 9, wherein the rotary die ismounted on a shaft slightly offset relative to a shaft centre, whichpermits pressing of sections of varying cross section.
 11. A deviceaccording to claim 10, wherein the means for varying the cross-sectionalarea consist of at least one supporting surface moveable transversely ofthe pressing direction.
 12. A device according to claim 10, wherein themeans for varying the cross-sectional area are synchronised with therotary die.
 13. A device according to claim 12, wherein the means forvarying the cross-sectional area consist of at least one supportingsurface moveable transversely of the pressing direction.
 14. A deviceaccording to claim 9, wherein the means for varying the cross-sectionalarea consist of at least one supporting surface moveable transversely ofthe pressing direction.
 15. A device according to claim 1, wherein therotary die is arranged to be lockable in a predetermined position.
 16. Adevice according to claim 15, wherein the rotary die has smooth portionswhich, in the locked position, are oriented towards the blank, so that,in this position, the blank passes the locked die to form a smoothsectional segment.
 17. A device according to claim 1, wherein the rotarydie is driven.
 18. A device according to claim 1, wherein extrusionpressure caused by the fixed die is maintained between the opening andthe rotary die.
 19. A device according to claim 1, wherein essentiallyno gap is formed between the opening and the rotary die.
 20. A methodfor pressing a plastically deformable blank into a three-dimensionalsection with a predetermined cross-sectional area, comprising pressingthe blank past at least one rotary die having one or more recesses inits peripheral surface, so that the blank is formed by the rotation ofthe die, thereby determining the final shape of the three-dimensionalsection, wherein the blank is caused to pass an opening immediatelyupstream of the rotary die, whereby the blank, when passing through theopening, is substantially reduced down to the predeterminedcross-sectional area.
 21. A method according to claim 20, wherein thecross-sectional area of the opening is varied according to the shape ofthe rotary die and the predetermined cross-sectional area of thethree-dimensional section.
 22. A method according to claim 20, whereinthe rotary die is locked in a predetermined position, so that, while therotary die is locked, the blank is pressed into a section withouttransverse sectional parts.
 23. A method according to claim 21, whereinthe rotary die is locked in a predetermined position, so that, while therotary die is locked, the blank is pressed into a section withouttransverse sectional parts.
 24. A method according to claim 20,comprising maintaining extrusion pressure caused by the fixed diebetween the opening and the rotary die.
 25. A method according to claim20, wherein essentially no gap is formed between the opening and therotary die.
 26. A device for continuously pressing of a plasticallydeformable blank into a three-dimensional section with a predeterminedcross-sectional area, comprising a fixed die with an opening formedtherein, through which the plastically deformable blank is intended tobe pressed, and at least one rotary die arranged immediately downstreamof the opening and having one or more recesses in its peripheral surfacefor forming the blank into a three-dimensional section with transversesectional parts during the rotation of the die, wherein: the rotary dieis located within a cavity formed in the fixed die.
 27. A deviceaccording to claim 26, wherein extrusion pressure caused by the fixeddie is maintained between the opening and the rotary die.
 28. A deviceaccording to claim 26, wherein essentially no gap is formed between theopening and the rotary die.
 29. A method for pressing a plasticallydeformable blank into a three-dimensional section with a predeterminedcross-sectional area, comprising pressing the blank through an openingin a fixed die past at least one die rotatably arranged around an axisextending transversely of the pressing direction and having one or morerecesses in its peripheral surface, so that the blank is formed by therotation of the die, thereby determining the final shape of thethree-dimensional section, the rotary die being located within a cavityformed in the fixed die.
 30. A method according to claim 29, comprisingmaintaining extrusion pressure caused by the fixed die between theopening and the rotary die.
 31. A method according to claim 29, whereinessentially no gap is formed between the opening and the rotary die.